1. Field of the Invention
This invention relates to a liquid distributor, preferably for a substantially vertical reactor containing a fixed catalyst bed, more particularly a tube-bundle reactor, the distributor being in the form of a channel distributor with drainage outlets.
2. Description of the Related Art
Liquid distributors of the type in question are used for material and heat exchange columns on the one hand and for reactors on the other hand and are intended to distribute the liquid over the packings or fixed beds arranged in the columns or reactors. In both cases, an important requirement is uniformity of distribution over the entire cross-section of the reactor or column independently of the load and a possible sloping position. More particularly, the efficiency of industrial trickle-bed reactors is influenced by the liquid distribution system. A uniform distribution of the liquid over the cross-section of the reactor guarantees adequate contact between the catalyst and the liquid phase and is therefore critical to the optimal operation of the reactor. If the volume of liquid is locally reduced by uneven distribution, performance is affected and has to be restored by an increase in temperature. However, this measure leads to losses of selectivity, to residue formation, to deposits and to caking of the catalyst. The outcome of this is failure of part of the catalyst packing. Since, in this case, the pressure loss in the packing increases beyond permitted limits despite high activity, the service life of the catalyst is reduced. Tube-bundle reactors in particular require a highly uniform distribution of the liquid to the individual tubes because any low-load regions are far more difficult to compensate with more heavily loaded regions than in shaft reactors.
One of the main causes of uneven liquid distribution is the blockage of the drainage outlets by soil present in the liquid. Other causes are the different distances of the drainage outlets from the point of introduction of the liquid, non-horizontal alignment of the distributor and variations as a function of time both in pressure and in the liquid flow rate on entry.
The problem addressed by the present invention was to provide a liquid distributor of the type mentioned at the beginning in which the uniformity of distribution of the liquid would be largely unaffected by the factors mentioned.
According to the invention, the solution to this problem is characterized by a cleaning arrangement with cleaning elements, more particularly pins, designed to be lowered into the opening of the drainage outlets. According to the invention, therefore, deposits and incrustations on the inside of the openings are mechanically removed from the drainage outlets. More particularly, one pin is associated with each opening.
Even if the pins are not exactly aligned, cleaning can still be carried out providing the pins are suspended from springs, more particularly helical springs.
Actuation of the pins is simplified if the pins are fixed to a holder which is designed for vertical displacement in a guide. Through the vertical displacement of the holder, all the pins can be simultaneously lowered into and also removed from the openings of the drainage outlets.
At rest, the holder should remain in an upper position. Accordingly, one particular embodiment of the invention is characterized by the provision of at least one spring element, which keeps the holder in an upper position, and an actuating element for depressing the holder. Accordingly, the cleaning arrangement need only be driven during the cleaning process. The rest position is automatically assumed between two cleaning operations.
To guarantee particularly trouble-free operation of the cleaning arrangement, the position and spring constant of the spring elements are coordinated so that, even if the holder is unevenly depressed, it does not jam in the guide.
The actuating element is preferably pneumatically driven. In this case, the holder with the cleaning pins is forced downwards when air is admitted and returns automatically to its rest position on venting.
In one particular embodiment of the invention, the cleaning arrangement is positioned inside the distributor and is designed to withstand high pressures. Accordingly, the cleaning operation can be carried out under pressure as often as required without any break in operation.